Sodium nitrate stabilized with colloidal asbestos



United States Patent O US. Cl. 252-21 2 Claims ABSTRACT OF THEDISCLOSURE Colloidal asbestos stabilizes finely divided sodium nitriteso that it can be dispersed in oil to form a concentrate which can beadded as a rust inhibitor to lubricating grease.

This invention relates to oil dispersions of sodium nitrite containingcolloidal asbestos as a stabilizer.

The use of sodium nitrite as a rust preventive in lubricating grease isknown. This rusting can be caused by water or moisture which may becomeabsorbed or entrained in the grease during use or actually rejected bywater repellent greases, thus directly contacting metal surfaces.However, while a number of methods have been proposed for incorporatingsodium nitrite into lubricating grease, these prior methods have hadvarious disadvantages. One such prior method involved mixing an aqueoussolution of sodium nitrite into the lubricating grease and then heatingto evaporate the water to thereby obtain a homogeneous dispersion of thenitrite in the grease. However, if the grease contains a soap or salt ofa metal other than sodium, particularly divalent metals, then metathesisoccurs at the high temperature necessary for the evaporation of thewater. The result is that metal of the soap or salt thickener isexchanged by sodium, thereby changing the characteristics of theoriginal grease. This has been found particularly objectionable in themanufacture of alkaline earth metal greases, e.g., calcium soap grease,since the structural stability of the grease is downgraded by metathesiswith the sodium nitrite. Another disadvantage ofthis method is thatsodium nitrite crystallizes out of the aqueous solution in the form ofrather large particles or crystals. These particles give the grease agrainy texture, as well as increasing its wearing tendency due to theabrasive nature of the sodium nitrite particles, and when used inbearing lubrication, give a noisy operation.

Another prior method of dispersing sodium nitrite in grease is disclosedin US. Patent No. 2,738,329. Here, the grease with sodium nitritepresent is heated to form a hot, fluid composition, i.e., heated to atemperature above the melting point of the grease. It was found that upcooling of the composition, the dropping point of the grease was verymaterial increased and other changes effected, even by the addition ofsmall amounts of sodium nitrite. Apparently some form of complex wasformed between the grease thickener and the sodium nitrite. However,this method is not applicable where the aim is only to increase the rustresistance of the grease, but not to alter any of its other properties.

Another prior method involves the simple addition of powdered sodiumnitrite into a finished grease composi tion with stirring. However, thismethod, even though the resulting composition si homogenized, results ina grainy grease and increases its wearing tendency and frequently causesnoisy bearing operation.

Other methods have involved rather complicated procedures of chemicallysub-dividing the sodium nitrite into fine particles by precipitation inthe presence of protective materials which coat the finely-dividedparticles to pre- ICC -vent their later agglomeration, since Withoutsuch a coating, the particles will cake upon storage. Prior methods ofmechanically grinding the sodium nitrite to a small particle size, e.g.,35 microns or less, are taught in US. Patent 3,078,226. However, thesodium nitrite prepared in this manner has to be freshly used, or ifstored, can be stabilized with Cab-O-Sil, which is a finely dividedpyrogenic silicon dioxide, but which is relatively expensive.

In the method of the present invention, sodium nitrite can be preparedin large quantities and kept in storage for later use. It can be lateradded to a grease without affecting any of the other properties of thegrease except inhibiting rusting caused by entrained water. Furthermore,a smooth, homogeneous, non-grainy grease product is obtained due to thefine particle size of the sodium nitrite. In this novel method,commercial granular sodium nitrite is dried and pulverized ormicronized, e.g., ground to below 60 micron particle size, followed bydispersion in mineral oil using colloidal asbestos as a stabilizingagent, to form a concentrate. This concentrate is stable and can bestored for extended periods of time without caking or particle growth.The concentrate can be easily added to a finished grease composition, orcan be added during the formation of the grease, but preferably afterdehydration to avoid metathesis. The colloidal asbestos is much lessexpensive than the aforesaid Cab-O-Sil, and in addition has rustpreventing properties of its own. Or alternatively, a dry mixturecomprising a major amount of sodium nitrite and about 1 to 12 wt.percent colloidal asbestos, based on the weight of the total mixture,can be prepared by simply pulverizing the sodium nitrite in the presenceof the asbestos to thereby give a free flowing stable mixture, which canlater be added to oil or grease.

Specifically, sodium nitrite is pulverized, as by ball milling, to anaverage particle size of 5 to 60, preferably 5 to 40 microns. Duringthis grinding, the heat of grinding will usually evaporate water so asto result in a very dry sodium nitrite having a low water content(usually less than about 0.1 wt. percent water). Colloidal asbestos canbe present during the pulverizing step as it appears to help dry out thesodium nitrite by taking up water. Sodium nitrite is very hygroscopicand tends to rapidly pick up water upon exposure to air with theresulting formation of hard granular particles or aggregate. Therefore,it is usually best to use freshly ground sodium nitrite, which alongwith colloidal asbestos, is added to the oil, e.g. lubricating oil. Theresulting concentrate will generally comprise: oil, about 10 to 60 wt.percent sodium nitrite, and about 1 to 12 wt. percent (based on theweight of said nitrite) of colloidal asbestos. Preferred concentrateswill comprise oil, about 30 to 60 wt. percent sodium nitrite, and about2 to 8 wt. percent, based on the amount of nitrite, of colloidalasbestos.

The use of natural asbestos as an ingredient of lubricating compositionsis quite old in the art and a number of various grease formulations aretaught in the book Lubri eating Grease by C. J. Boner, 2nd edition,pages 687 et seq. These prior greases utilized natural asbestos orasbestos floats, both of which are relatively long fibered asbestos.However, this fibered asbestos was always used in conjunction with otherthickening agents such as soaps, since the long fibered asbestos willnot form a thickened homogeneous grease gel by itself, but rather reliesupon other ingredients to form the grease or gel-like structure. Theasbestos of the present invention differs from the aforesaid longfibered conventional asbestos in that the asbestos particles are in avery small colloidal size, having a large surface area, and can bedispersed in the oil to form a gel by itself, and without settling outfrom the oil. This colloidal asbestos is chrysotile having the chemicalformulation Mg (OH) Si O The usual mode of occurrence of chrysotile is across-fiber configuration in which filaments of chrysotile (i.e. bundlesof fibers) are closely packed together and set at right angles to thewalls or cracks and fissures that extend through the host rock of theore body. However, in 1959, an unusual deposit of chrysotile asbestos,with properties and a mode of occurrence different from the previouslyknown cross-fiber material, was discovered in central California. Theore of the new deposit, instead of occurring in veins, occurs inrandomly-oriented, matte-like flakes and agglomerates of visibleasbestos filaments, which in turn are made up of many thousands ofextremely small tubular fibers. The lengths of these small fibers varyfrom a few millimicrons to thousands of millimierons, generally 2,000 to30,000 millimicrons, while the diameters of the fibers vary much lessand are usually in the range of 1 to 800, e.g., 10 to 400, millimicrons.A typical colloidal asbestos that was used in the working examples ofthe invention had the following characteristics:

Properties of colloidal asbestos fibers Brightness (GE) 74-76.Refractive index 1.55. Dispersion in water Fully/ pH range 46. Surfacearea 47-50 sq. meters/gram. Oil absorption 14-16 cc./10 grams of fibers.Water retention 42 grams/20 grams of fibers. Dry bulk density 22.5lbs/cu. ft. Fiber dimension:

O.D. 25.0 millimicrons. I.D. 6.0 millimicrons. Length 2,50025,000millimicrons.

Sodium nitrite in amounts of 0.5 to 3.0 wt. percent, preferably 1.5 to2.5 wt. percent, based on the weight of the total composition, may beused in any of the common lubricating greases. Usually about 1 to 12 wt.percent, based on the weight of sodium nitrite, of colloidal asbestoswill be used to stabilize the nitrite in the grease. Included aregreases wherein lubricating oil is thickened with salts, soaps,soap-salt or mixed salt complexes, polymeric thickeners (e.g. polymersof C to C monoolefins of 10,000 to 200,000 Staudinger molecular weightsuch as polyethylene) and inorganic thickeners (e.g. clay, carbon black,silica gel, etc.). However, the method of the invention is of particularvalue in cases where the grease is thickened with a metal soap otherthan sodium, and particularly where the metal is an alkaline earth metalsuch as calcium.

Generally, the greases will comprise a major amount of either asynthetic or mineral lubricating oil, thickened with about 3 to 49 wt.percent, usually 20 to 45 wt. percent, of a thickener. In the case ofsoap-salt and mixedsalt thickeners, the thickener is usually formed byconeutralization in oil, by metal base, or various mixtures of highmolecular weight fatty acids and/or intermediate molecular weight fattyacids with low molecular weight fatty acids.

The high molecular weight fatty acids useful for forming soap, soapsaltand mixed-salt thickeners include naturally-occurring or synthetic,substituted and unsubstituted, saturated and unsaturated, mixed orunmixed fatty acids having about 14 to 30, e.g., 16 to 22, carbon atomsper molecule. Examples of such acids include stearic, hydroxy stearic,such as l2-hydroxy stearic, dihydroxy stearic, polyhydroxy stearic andother saturated hydroxy fatty acids, arachidic, oleic, ricinoleic,hydrogenated fish oil, tallow acids, etc.

Intermediate molecular weight fatty acids include those aliphatic,saturated, unsubstituted, monocarboxylic acids containing 7 to 12 carbonatoms per molecule, e.g., capric, laurie, caprylic, nonanoic acid, etc.

Suitable low molecular weight acids include C to C fatty acids. Aceticacid or its anhydride is preferred.

Metal bases which are frequently used to neutralize the above acids arethe hydroxides, oxides or carbonates of alkali metals (e.g., lithium andsodium) or of alkaline earth metals (e.g., calcium, magnesium, strontiumand barium).

Various other additives may also be added to the lubricating composition(e.g., 0.1 to 10.0 wt. percent based on the total weight of thecomposition) for example, oxidation inhibitors such asphenyl-alpha-naphthylamine; tackiness agents such as polyisobutylene;stabilizers such as aluminum hydroxy stearate; and the like.

The following examples further describe the invention wherein all partsare parts by weight.

Example I Part A.Two parts of the previously described colloidalasbestos and 49 parts of a coarse commercial sodium nitrite were milledtogether in a ball mill for 16 hours until the sodium nitrite wasreduced to an average particle size of about 35 microns. The milledmixture of asbestos and sodium nitrite was then removed from the ballmill, and mixed with 49 parts of a mineral lubricating oil having aviscosity of 55 SUS at 210 F.

Part B.A sample of the mixture of Part A was stored at room temperaturein a closed container for three months. At the end of this time, therewas no settling of the sodium nitrite or asbestos from this oil.

Part C.-A sample of the dry mixture of 49 parts of sodium nitrite and 2parts asbestos taken from the ball mill after 16 hours in Part A,without oil, was kept in a closed container to keep out moisture andstayed dry and showed no tendency to cake after storage for 24 months.It remained free flowing.

Part D.-In comparison, a sample of the same sodium nitrite pulverized tothe same particle size in the ball mill, but without asbestos present,caked on standing overnight even though kept in a closed container.

Parts A and B illustrate that the colloidal asbestos will stabilize oildispersions of sodium nitrite against separation. Parts C and D showthat the asbestos acts to prevent caking of sodium nitrite.

Example II Part A.A lubricating grease was prepared as follows: A greasekettle was charged with 55.6 parts of mineral lubricating oil having aviscosity of 55 SUS at 210 F., and 10 parts of tallow fatty acid havinga saponification number of 192 and a Wijs iodine number of 54. Then 13.4parts of hydrated lime were added to the kettle, while mixing untilsmooth and homogeneous. Then, glacial acetic acid was slowly added tothe kettle while maintaining the temperature of the kettle contentsbelow about 200 F. External heating was then applied to the kettle andthe contents were heated to about 325 F. to dehydrate the reactionproduct. One part of phenyl-alphanaphthylamine was added as anantioxidant, following which the product was rapidly cooled from 325 F.to F. by circulating cooling water through the kettle jacket. Then, 2wt. of sodium nitrite pulverized to an average micron size of 30, whichhad been standing 20 days in storage after pulverizing, was added to thegrease product. The grease was then homogenized by passing through aCharlotte mill having a clearance opening of about .002". The resultinggrease product was grainy due to the presence of hard, large sodiumnitrite particles caused by reagglomeration of the pulverized sodiumnitrite.

Part B.-A grease was prepared in the same manner as in Part A, butinstead of using the two parts by weight of sodium nitrite per se, therewas used instead a dispersion consisting of two parts by weight of thepulverized nitrite (average size of 30 microns) dispersed in two partsof the mineral lubricating oil. This dispersion, after two weeksstorage, had separated with the sodium nitrite settling out as a hardmass 011 the bottom of the container. This showed that even thoughprotected by oil, the sodium nitrite agglomerates. With much difiiculty,and with vigorous stirring, it was possible to redisperse the Grease Bgave good results, but the sodium nitrite had separated from the oil andwas very diflicult to redisperse. Greases C and D, representing theinvention, formed smooth homogeneous greases and gave no noise in theBearing Noise Test, while at the same time there nitrit so it ld b dd dto h grease 5 was no d'ifiiculty with the sodium nitrite separating asin Part C.A grease was prepared in the same manner the Case gffiase asshown in Part A, except there was used 2.0% of a What Z P 1s: i mixtureconsisting of 49 parts of dry pulverized sodium 1 h i i compnsmg malo?amountpf nitrite stabilized with two parts of the aforesaid colloidal 55 2 t ene i fi i g FE asbestos, which mixture had been in storage fortwo u .pfircen 0 me a sa 0 a Weeks in aipticht drums The condition ofthe Sodium wherein said metal is selected from the group consisting 0red of alkali and alkaline earth metals, as grease thickener, m nevgsunca an 1 C u h and containing 0.5 to 3.0 wt. percent of sodium nitritePart grease Was prepare e m manna: as having an average particle sizeless than about 60 mi- 111 Part A, P P that 2% Sodlum mtrlte-colloldlcrons, and as a stabilizing agent for said nitrite, about asbestosmixture was added in the form of the oil dis- 1 to 12 wt percent, basedon the weight of Said Sodium persion of Example I, Part A. nitrite, of afinely divided colloidal asbestos having par- Th cOmPOSItlOIlS andproperties of the greases of ticle outer diameters of about 1 to 80millimicrons and Example II are summarized in the following table:particle lengths of about 2,000 to 25,000 millimicrons.

TABLE Example II A B 0 D Composition (Parts by Weight):

Glacial acetic acid 8. 18.0 18.0 18.0 Tallow fatty acid 10. 10. 0 10.010.0 Hydrated lime 13- 13. 4 13. 4 13. 4Phenyl-alpha-naphthylamine 1. 1. 0 1. 0 1. 0 Sodium nitrite of micronaverage size 2. 2. 0 1. 92 1. 92 Colloidal asbestos 0. 0.0 0.08 0. OSMineral lubricating oil of 55 SUS at 210 F 55. 6 55. 6 55. 6 55.6Properties:

Appearance Grainy Smooth Smooth Smooth ASTM Cone Penetration, 77 F.:

Unworked 320 325 325 320 Worked 60 Strokes 320 325 325 325 Worked 10,000Strokes 329 329 322 322 Timken E.P. Test (lbs. load carried) 45 45CRC-L-41 (14 Day Corrosion)- Pass Pass Pass Pass Bearing Noise Noisy NoNoise No Noise No Noise The CRCL-41 Test was carried out by coatingchemically clean Timken bearings (cup and bearing) with a thin coatingof the grease and subjecting the hearings to turning at 600 r.p.m. undera load to spread the grease in a thin layer. The cup and bearingassembly were then dipped in water and stored for 14 days in a closedglass jar containing a small amount of water so as to maintain a humidatmosphere. After that, the bearing was then examined for rust.

The Bearing Noise Test was carried out in a soundproof room, measuringthe noise level obtained during operation of a Timken roller bearing.

While the compositions containing sodium nitrite gave no rust in theCRC-L-41 Test, a similar grease containing no sodium nitrite agentresults in bad rusting of the bearing.

As seen in the table, in greases A to D, the sodium nitrite impartedrust inhibition to the greases as indicated by the 14-day CorrosionTest. However, grease A was grainy and resulted in bearing noise, thusindicating that the sodium nitrite was in large particle sizes.

2. A grease according to claim 1, wherein said oil is a major amount ofmineral lubricating oil, said thickener is about 20 to 45 Wt. percent ofcalcium mixed salts of acetic and higher fatty acid, the amount ofsodium nitrite is about 1.5 to 2.5 wt. percent based on the weight ofthe total grease composition, and said asbestos has a particle outerdiameter of about 10 to 40.0 millimicrons.

I VAUGHN, Assistant Examiner US. Cl. X.R. 252-25, 387

